1. Field of the Invention
The present invention relates to performing a spectral analysis of a signal in a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Data is written by applying a current to a write element of the heads. The write current is set in accordance with various parameters such as overshoot duration. Likewise a read element has a defined bias voltage that is set at an optimal value.
The heads are separated from the disk surfaces by air bearings. The air bearings minimize contact between the heads and disks to reduce component wear. The air bearings are described in terms of a flying height. The magnetic field strength is inversely proportional to the flying height. An increase in flying height will cause a decrease in the magnetic field sensed or used to write information on the disk.
It has been found that analyzing the read signal to determine harmonics at specific frequencies can be useful in determining and optimizing certain operating parameters such as the write current, bias voltage and flying height control. By way of example, U.S. Pat. No. 5,784,296 issued to Baker et al. describes a harmonic sensor that is used to accumulate sampled data taken from a read signal of a disk drive. A spectral analysis is then performed on the accumulated sampled data to determine various harmonics at certain signal frequencies. The effective bandwidth of the harmonic sensor becomes very narrow when there are long sample sequences. The sensor becomes more sensitive to sample frequency when accumulating long sample lengths. Such sensitivity can lead to errors if the samples are not taken at the correct time.